The present embodiments relate to an x-ray system having a C-arm and a method for compensating for a deformation and/or oscillation of a C-arm.
The C-arm of an x-ray system is loaded by the dead weight of components fastened to the C-arm (e.g., an x-ray emitter, a detector, a diaphragm and a grid). On account of a finite rigidity of the C-arm, the C-arm is deformed by the dead weights. The C-arm may also oscillate in its entirety due to dynamic loads. Several problems are caused as a result.
The components move toward one another on account of static deformations of the C-arm, which, particularly in 3D reconstructions, results in a falsification of the x-ray image recordings. Dynamic loads on account of inertia forces result in unwanted oscillations of the C-arm, as a result of which the alignment relative to the isocenter is disturbed. The use of innovative components such as, for example, a high focusing grid that requires a very precise alignment is hampered. Oscillations occur on account of the finite rigidity of the C-arm. The oscillations have a negative affect on the image quality and the examination time. These effects are very disruptive (e.g., in the case of a C-arm angiography system).
It is known from the prior art to improve the rigidity of the C-arm by the geometry of the C-arm being optimized. Attempts are made to keep the deformations as low as possible in all directions by a larger cross-section of the C-arm. Solutions of this type result in the C-arm becoming larger and heavier, thereby causing problems. The weight of the C-arm is increased by a larger cross-section, as a result of which the dynamics of the C-arm movement is negatively affected. Both the maximum speed and the acceleration are reduced. The available space reduces on account of the larger cross-section with an identical C-arm length, as a result of which the accessibility in terms of the patient worsens with specific examinations. The fitting of heavy components requires an even larger cross-section of the C-arm, as a result of which the weight is increased again. An upper limit is imposed in terms of optimization of the cross-section.
With known x-ray devices such as disclosed, for example, in DE 10 2008 003 815 A1, the C-arm is arranged on a stand that is, for example, vertical on the base side and may be rotated about a usually horizontal axis via a swivel guide. In the swivel guide, the C-arm is rotatable about an isocenter along an arc-shaped guiding path of the C-arm. A particularly light C-arm is to be used in order to achieve the best possible dynamics in applications, in which the C-arm is moved with significant speed along the swivel guide. An angiography x-ray device is an example. For this reason, C-arms made of extruded sections that include a rectangular hollow profile in cross-section may be used.
Instead of a floor stand and connecting the C-arm via the swivel guide, as a result of which the required degrees of movement freedom for the C-arm movement and positioning is realized, it is known to arrange the C-arm on an industrial robot with a robot arm and a corresponding control device. With such an embodiment, the degrees of freedom are provided by the six axes of movement of the robot. The C-arm is rotationally mounted directly on the robot arm.
DE 10 2005 018 326 A1 discloses the creation of a sharp x-ray image using an x-ray emitter or x-ray receiver that may be moved with respect to a holding position by a drive device despite a system structure that may be made to oscillate using a resonant frequency that is dependent on the respective holding position. In this process, at least one variable dependent on the respective holding position and relevant to the resonant frequency is detected. A desired movement control that counteracts the oscillation is determined in order to achieve a movement state of the x-ray emitter or x-ray receiver provided for the x-ray examination as a function of the at least one respective variable and the movement of the x-ray emitter, or the x-ray receiver is controlled by the drive device in accordance with the desired movement control.
DE 10 2011 005 492 A1 describes an x-ray apparatus with a C-arm, on which an x-ray source and an x-ray detector may be attached in the opposite arrangement, at least one actuator for positioning the C-arm relative to a mounting facility, and a control device for controlling the actuator. The x-ray apparatus includes at least one sensor that, at a first position of the C-arm, detects a deformation of the C-arm and transforms the deformation into an output signal. The deformation of the C-arm may be influenced by a force exerted by an operator and directly or indirectly affecting a second position on the C-arm. The control device influences the actuator as a function of the output signal of the sensor.
DE 101 61 152 A1 discloses a radiation therapy system having a hexapod unit, on which a collimator is arranged.